In a magnetic disk drive such as hard disk drive, when rotational vibration is applied to a disk housing due to a shock from the outside, disturbance caused by such rotational vibration may act on a positioning control system of a magnetic head, which possibly interferes with positioning of the magnetic head. Therefore the magnetic disk drive has been applied with a measure for compensating the disturbance caused by the rotational vibration of the disk housing.
For example, Japanese Patent Publication No. 2001-14782(“patent document 1”) discloses a magnetic disk drive in which a rotational vibration detector for detecting rotational vibration of a drive housing is provided, and a feed-forward control system for outputting a signal for compensating disturbance according to detected rotational vibration is incorporated in the positioning control system of the magnetic head.
When the rotational vibration detector is provided in the magnetic disk drive, an output signal from the rotational vibration detector may contain a disturbance component due to mechanical resonance of the rotational vibration detector (hereinafter, called resonance disturbance component). Therefore, the resonance disturbance component needs to be suppressed.
However, since mechanical resonance frequency of the rotational vibration detector is different depending on production lots, the resonance disturbance component contained in the output signal from the rotational vibration detector is hard to be suppressed. For example, when a filter (so-called notch filter) is used for suppressing a signal component in a specific frequency band, a frequency of the resonance disturbance component is possibly deviated from the specific frequency band of the filter, and consequently the resonance disturbance component may be hardly suppressed. Moreover, when the specific frequency band of the notch filter is widened in order to suppress the resonance disturbance even if there is the variation in mechanical resonance frequency, phase delay in the output signal possibly becomes too large to enhance the disturbance compensation by the feed-forward control system.